The following formula (I) can be attributed to the phenyl pyruvic acids obtainable according to the present invention: ##STR1## wherein n is an integer selected from 1, 2 and 3, and substituent or substituents R, like or unlike one another, are hydrogen, alkyl or alkoxy groups having 1 to 4 carbon atoms, in their turn also substituted by alkoxy groups having 1 to 4 carbon atoms, or they are halogens, nitrile groups, acyl groups, etc.
Several methods of preparing phenyl pyruvic acid have been proposed, such as the transposition of phenylglycidic acid with concentrated HCl, the hydrolysis of ethyl phenyloxalacetate, the condensation of N-diethyl-oxamic ester with benzyl-magnesium bromide, etc.
These methods, however, besides being alien to the process of the present invention, due to the complexity of the production steps involved, the uncommon starting materials and reactions required, and the yields not always profitable, have few possibilities of being actually applied to an industrial scale.
Processes have also been described for preparing phenyl pyruvic acids by carbonylation of benzyl halides, also substituted, with CO under pressure in the presence of a carbonylation catalyst, such as the salts of the hydrocarbonyl compounds of Fe, Co and Ni, the carbonyls of Fe, Ni or Co in an alcoholic-aqueous medium, and of a base consisting of oxides and/or hydroxides of alkaline earth metals.
However, in the last-mentioned processes, the phenyl pyruvic acids are obtained in the form of a mixture with the corresponding phenylacetic acids (products of mono-carbonylation) which form simultaneously in a quantitative ratio. Therefore, to direct the reaction towards the highest possible selectivity in respect to the phenyl pyruvic acids (products of di-carbonylation) to be obtained, the actual operating conditions require operation with high pressures of gaseous CO, in any case not lower than about 50-60 atm. Furthermore, under such conditions, the quantitative ratio between phenyl pyruvic acid and phenyl acetic acid or substituted derivatives thereof is not always selective enough; for example for the non-substituted compound (phenyl pyruvic acid) the selectivity does not exceed a value of 4.5. In consequence, the maximum selectivity obtainable in phenyl pyruvic acid is rather low.